Those airplanes are essentially two-pilot airplanes which the FAA allows to be operated as single pilot by a specially trained pilot.

The generic type rating requires two pilots. You can get a one-pilot type by demonstrating that you can do it all by yourself.

If the PIC has a single-pilot type, he can still chose to operate with two pilots...legal and loggable SIC. The SIC would need the minimum training in part 61.